A really cool recent study from the University of Copenhagen, published in Scientific Reports, used miniature satellite tags to study the winter migration of cuckoos (Cuculus canorus) from Europe to Africa.

Just before winter migration was going to begin, researchers relocated 11 adult cuckoos from Denmark to Spain. Released more than 600 miles from their normal migration starting point, cuckoos were able to orient themselves in their new location and make complex, individual judgements about new migratory routes. The released birds headed towards diverse stopover points on the normal route, which the authors believe "indicates an ability to assess advantages and disadvantages of different routes, probably based on their health, age, experience or even personality traits. They evaluate their own condition and adjust their reaction to it," displaying complicated decision-making behavior never before documented in migratory birds.

To be able to make judgements about their route strategies, the cuckoos must be able to mentally balance the costs and benefits of different routes, which requires knowledge of their current location in relation to potential goals, and the distances to those goals. The researchers are hoping that future technological advances will allow for the creation of tags small enough to monitor young cuckoos on their first migratory journey.

Although this is not true of all cuckoo species, European Cuckoos are especially valuable for studies of bird navigation because they are "brood parasites"--which means adults lay eggs in the nests of other birds, who then raise the cuckoo chicks as their own. That means young cuckoos grow up without biological siblings or parents, and thus do not learn their migratory pathway from other adults of their species. Flying alone at night, they rely "entirely on instincts, inherent abilities and the experiences gained later in life."

You can read the press release from the University of Copenhagen here, which includes a video rendering of the normal cuckoo migration routes from Europe to Africa and the routes taken by the relocated birds.